1. Technical Field
The present invention relates to techniques for shifting a level of an input signal.
2. Related Art
A level-shift circuit for shifting a level of an input signal to generate an output signal having a shifted level is known. The level-shift circuit shown in FIG. 9 is disclosed in JP-A-7-98983 (FIG. 8). The level shift circuit includes a latch circuit having two inverters at an output stage. A p-channel transistor and an n-channel transistor are connected to an input node of the latch circuit. An input signal is supplied to the p-channel transistor and the n-channel transistor via two capacitive elements. When a threshold voltage of the p-channel transistor is Vthp, the gate is biased to VCC−Vthp by a resistor. When a threshold voltage of the n-channel transistor is Vthn, the gate is biased to VEF+Vthn by a resistor. Thus, when the level of the input signal rises, the n-channel transistor is changed to be in an ON state in synchronization with the rising edge of the input signal, and then the electric potential of the input node of the latch circuit is changed to be VEE. When the level of the input signal falls, the p-channel transistor is changed to be in an ON state in synchronization with the falling edge of the input signal, and then the electric potential of the input node of the latch circuit is changed to be VCC. Thus, an output signal is generated by shifting the level of the input signal.
However, a level-shift circuit of the related art has problems described below. First, because two capacitive elements are needed in the level-shift circuit of the related art, if such a level-shift circuit is built in an integrated circuit (IC), the footprint of the level-shift circuit becomes large. Second, because the latch circuit is inverted by using only a pulse supplied to the input node, if variations occur in driving characteristics of transistors while the transistors are being manufactured, the electric potential of the input node may not be changed sufficiently, thereby causing the level-shift circuit to operate improperly.